For example, in power generation equipment utilizing a steam turbine, heat energy of steam generated by a boiler is converted into mechanical work by the steam turbine, and a valve device is provided between the boiler and the steam turbine. The valve device forms a flow passage of the steam (fluid) fed from the boiler to the steam turbine, and opens and closes the flow passage by operating a valve element and bringing it in tight contact with part (valve seat) of an inner wall of the flow passage.
This valve device has a problem that the steam flowing from the boiler into the valve device (flow passage) hits the inner wall of the valve device as jet (see Patent Document 1). The steam hitting the inner wall of the flow passage causes pressure loss of the valve device and also causes erosion of the inner wall. Particularly, when the valve seat is eroded, a flow of steam flowing along the valve seat into the steam turbine may be disturbed.